Our overall goal is to perform experiments which will 1) provide insight into the synthesis and secretion of substances likely to be components of the internal extracellular layer of terminal lung units, 2) examine factors which modulate and influence these processes and 3) shed light on ultrastructural changes in cytoplasmic components of the pulmonary granular pneumocyte. We shall study the influence of hyperoxia, hypoxia, hormones and of alterations in pulmonary blood flow, ventilation and the autonomic nervous system on these processes and parameters. We anticipate that these experiments will generate information which will enlarge our understanding of the molecular and cellular basis for lung function at the organ level. We expect to achieve this objective using combined biochemical and ultrastructural stereological techniques to study protein synthesis and secretion by the lung. It must be stressed, however, that we are using these techniques on the lung because we are interested in the behavior of this organ and not because the lung affords a convenient model for the study of the fundamental biological processes involved.